This program was initiated to obtain in quantity homogenous populations of cells that possess transport properties of interest to the nephrologist. Cell lines currently in continous culture are surveyed for transport properties and responses to hormones and drugs similar to those of renal tubules. In addition to the established cell lines, we are attempting to start primary cultures of cells from different segments of the rabbit nephron and from the toad urinary bladder. Epithelial cells from the toad bladder have been grown in continuous culture for over a year. There is evidence of transepithelial transport by the cells.